Since the advent of continuous casting of slabs, the steel industry tried to successfully combine the hot strip mill and the continuous caster through an inline arrangement so as to maximize production capability and minimize the equipment and capital investment required. The initial efforts cast slabs 6 inches to 10 inches thick. These mills included a reheat furnace, a rougher and a six or seven stand finishing mill with a capacity of 1 1/2 to 5 million tons per year. It is unlikely that new hot strip mills of this design would ever be built due to the high capital cost and inflexibility as to product mix and thus market requirements.
These difficulties gave rise to the development of the so-called 2 inch or less thin slab continuous hot strip mill which typically produces 1,000,000 tons of steel per year as specialized products. However, thin slab casters have serious drawbacks regarding the quality and quantity limitations. These limitations are discussed in detail in parent application Ser. No. 08/123,149 filed on Sep. 20, 1993, which is herein incorporated by reference.
The integration of a slab caster with any hot rolling mill requires a synchronizing of the casting and rolling of slabs. Without the ability to decouple the casting and rolling of slabs in such an integrated system, a breakdown anywhere in the process stops the entire line, possibly resulting in the scrapping of the entire product then being processed. The casting and rolling of slabs can be effectively decoupled by providing the ability to transfer a cast slab to a slab storage area. However, this solution is inefficient. The slab is transferred to an external slab storage area such that when the mill is brought back on-line, a substantial amount of energy is required to bring the slabs back to an appropriate rolling temperature. Several other approaches have been attempted to address this particular problem. These include retaining or storing hot slabs in a heating furnace or in a thermal insulating chamber. However, these solutions have also had certain drawbacks including the space required and the capital expense involved.
It is an object of our invention to integrate an intermediate thickness slab caster with a hot reversing mill. It is a further object to adopt a system which balances the rate of the caster to the rate of the rolling mill and provides a slab storage container for decoupling the caster and the mill. It is also an object of our invention to adopt a system using less thermal and electrical energy. It is still a further object to adopt an automated system with small capital investment, reasonable floor space requirements, reasonably powered rolling equipment and low operating costs.